(1) Field of the Invention
This invention relates to a rust preventive resin composition suitable for use in formed or molded materials useful in covering, wrapping or packaging (hereinafter called "wrapping" collectively) various metal products which require rust prevention, such as films, sheets, tubes and other packaging containers.
(2) Description of the Prior Art
Sheets and films with a rust preventive applied thereto have conventionally been known.
They include, for example, sheet-like materials, such as paper and textile, with a rust preventive adhered or coated thereon or impregnated therein; films and sheets formed by subjecting a mixtures of a polyolefin-base resin and a rust preventive to melt extrusion molding; and the like.
The former rust preventive materials are however insufficient in rust preventive properties and the long acting property thereof in spite of the usual practice of incorporation of a rust preventive in relatively high contents, because the paper and textile as base materials have high breathability and moisture permeability by themselves. It is hence necessary to laminate a material having low breathability and moisture permeability, such as a polyethylene film, or otherwise to use an additional outer wrapping material, thereby resulting not only in complicated wrapping work but also in a disadvantage in respect to wrapping costs.
On the other hand, the latter rust preventive materials encounter difficulties in dispersing the rust preventive in the resin uniformly at high contents due to the poor compatibility of the rust preventive with the polyolefin-base resin. This approach is therefore accompanied by such drawbacks that it cannot provide films having high rust preventive properties and in addition, the transparency, heat-sealing characteristics and the like of the resultant films per se are deteriorated.
With a view toward overcoming such drawbacks, it has also been proposed to combine a polar resin such as ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer or ethylene-vinyl acetate copolymer with a polyolefin-base resin so as to produce a rust preventive film improved in the compatability and dispersibility of its associated rust preventive with respect to the resin (Japanese Patent Publication No. 4295/1972). Although films obtained in accordance with this process are free of exudation or bleeding and exhibit long-acting rust preventive effects, they involve some practical problems as rust preventive wrapping films for metal products since the polar resin is highly corrosive to non-polar resins such as polyethylene and its corrosive properties becomes remarkable especially when maintained in contact with metals. The above-mentioned corrosive properties of the polar resin can be reduced to a certain extent by using the rust preventive in a large amount. Such excessive use of the rust preventive however leads to another problem that the transparency and heat-sealing characteristics of films are inevitably deteriorated.
It has also been proposed to produce a rust preventive film by adding and mixing an organic amine and an acid with a polyolefin resin and then heating and melt-molding the resultant composition so that a volatile rust preventive consisting of the acid salt of the organic amine is formed by the reaction of the organic amine and acid in the course of the molding step, thereby allowing the rust preventive to be dispersed uniformly in the resin (Japanese Patent Publication No. 2449/1978). This process is very effective in dispersing the volatile rust preventive uniformly in the resin. It is however accompanied by such problems that the rust preventive undergoes bleeding to the surfaces of the film along the passage of time and hence deteriorates the transparency and heat-sealing characteristics of the film per se.